Conventionally, a structure on which an article is to be mounted has formed thereon a mounting member A as shown in FIGS. 8 and 9. The mounting member A includes a pair of webs 2 extending downwardly substantially parallel to each other from a lower surface of the structure 1, and a pair of flanges 3 extending mutually inwardly from and transversely to the lower ends of the webs 2 so as to define therebetween a slot 3a. It is to be noted that the structure shown in FIG. 8 serves as the floor of a vehicle and an article is required to be mounted upon the structure.
A groove 4 having a substantially rectangular cross section is defined by and between the webs 2 and the flanges 3 of the mounting member A, as well as by means of the lower surface of structure 1. A head 7 of a bolt B for fastening a flange 6 of an article 5 to the mounting member A is fitted within the groove 4, and the bolt B is fastened to the mounting member A by means of a nut 8 tightened upon the bolt B.
Accordingly, when the nut 8 is tightened onto the bolt B, it is necessary to prevent the bolt B from rotating about its axis. To this end, the head 7 of the bolt B is normally shaped and dimensioned so that it defines a closely toleranced fit within the groove 4. Thus, where the head 7 of the bolt B used has a regular square shape, either a method wherein the head 7 is inserted into the groove 4 from one end thereof and then slid therealong to a predetermined position of the groove 4 or another method wherein a cutaway portion 9 for admitting the head 7 of the bolt B therethrough is provided at a suitable position of the flanges 3 may be used. However, according to the former method, the head 7 of the bolt B cannot be inserted into the groove 4 if the end portion of the groove 4 is blocked, while according to the latter method, a manufacturing step for forming the cutaway portion 9 is required and the article 5 cannot be mounted at the position of the cutaway portion 9.
In order to resolve such disadvantages as described above, a method as illustrated in FIG. 8 has also been devised wherein the head 7 of the bolt B has a deformed rectangular or substantially parallelogram shape such that the width or the dimension of the shorter side thereof may allow the head 7 to be inserted through the slot 3a between the flanges 3 and the head 7 after having been disposed within the groove 4 may be turned through means of an angle of approximately 90 degrees about its axis in the direction indicated by the arrows within the groove 4 until it is closely fitted within the groove 4. It is self-evident that this method involves a complexly shaped head 7 of the bolt B, which results in high production costs for the bolt B.
Furthermore, in the case of the mounting member A described above, when the article 5 is secured thereto, the stress at the crossing or connecting corner portions 10 defined between the flanges 3 and the webs 2 is increased so that where the mounting member A is formed by extrusion molding of a conventionally used aluminum material, as shown in FIG. 11, a crack C may appear at such corner portions 10 depending upon the fastening torque or the condition of the load applied thereto, which will be a significant problem with respect to the mechanical strength of the mounting member A.